October 2010 archive

October's pick of web video features 10 science and tech shockers guaranteed to tingle your spine. Watch in terror as slime mould overruns Tokyo. Cower before the most awesome destructive force in the universe - a supernova. Watch out for all the usual Halloween favourites: bats, snakes, crows, skeletons and body parts. And for all you zombies out there, the number 1 clip promises to be delicious.

Imagine a dog walking behind a picket fence. Only sections of moving dog are visible, but without having to think about it you know there's a whole dog there. How the brain manages this trick is still unclear, but Peter Scarfe from University College London has come up with some interesting illusions while trying to understand the rules that the brain applies to moving objects.

In the video above, three circles seem to be lined up. When the video is played, and lines within the shapes begin to move, the row of objects appears to shift and become misaligned. Pause the video, however, and the objects are clearly in a row. "Even if we hold a ruler up to the screen and prove to ourselves that these objects are aligned with one another, we still perceive them as misaligned," says Scarfe.

"Normally, in our everyday world, objects change position when they move. This illusion represents a special case where we have an object producing motion in a given direction, but staying stationary."

One explanation is that the brain is "tuned" to the likelihood of the environment behaving in a certain way. For example, the visual system can make a good guess that moving objects will probably change position, says Scarfe, because a person will encounter this many times in everyday life. The illusion may therefore occur because the brain's prior knowledge about the world influences perception.

In the second part of the video, a number of circles are grouped into two blocks. When each circle has moving stripes inside it, the two blocks appear to shift out of line with each other - effectively, the two groups start to act like separate objects.

This illusion could be likened to snow falling. Each snowflake is drifting in a different direction, but the overall effect is that the snow is falling vertically. "The brain has some understanding of which signals to group together," says Sharfe, and these illusions should help to explain how the brain applies these rules, and at what stage of the visual system. "That is what we are hoping to find out by using these stimuli," he says.

Stare hard at the spiral. Does it affect how you perceive the woman? If you don't see it first time, try watching again in full screen.

Swirling spirals and a feminine eye might remind you of the title sequence of Alfred Hitchcock's Vertigo, but now psychologists are using those same images to investigate the rules of attraction.

In the video above, created by Clare Sutherland and Rob Jenkins from the University of Glasgow, UK, a woman's pupil appears to dilate, even though the image is a still photograph. The trick is down to a powerful after-effect caused by staring at a rotating spiral, positioned in exactly the same part of the screen as the pupil, before seeing the photograph of the woman.

If dots on a screen are surrounded by certain types of moving pattern, fixing your eyes on one of the dots can make the others disappear.

This illusion, called motion-induced blindness, was discovered 20 years ago but psychologists are still trying to understand why it happens. One possible explanation is that our visual system receives so much information at any given moment that we cannot process it all, so we remain unaware of it.

Now Erika Wells and Andrew Leber from the University of New Hampshire have come a step closer to the answer after investigating how two different moving backgrounds affect the illusion.

In one version, fixed dots are surrounded by pixels that all move in the same direction. In the other, the background elements move randomly in different directions (see video above). Until now, most research has focused on the first set-up, says Wells, but by comparing the two versions the team are gaining new insights.

They found that that the illusion was more pronounced, and the yellow dots disappeared more readily, when the background pixels moved randomly. This could be because different parts of the visual cortex process these two types of motion.

"Incoherent motion is processed lower down in the visual cortex than coherent motion," Wells says. "It may be that the signals coming from the early visual areas are 'noisier'," she says. Noisier signals arriving in higher visual areas may be harder to interpret, distracting the brain from the target and so making it more difficult to detect.

The artist M. C. Escher was renowned for creating drawings of imaginary spaces that could not exist in three dimensions. Or could they?

Kokichi Sugihara at Meiji University in Kawasaki, Japan, has been using computer software to bring impossible drawings to life. The video above shows some of the objects he has made moving in ways that appear to defy geometry.

When the models are turned around, however, the trick is revealed: the objects are not what they seem. That's because we constantly make assumptions about perspective and depth in order to move about in a 3D world, and these models take advantage of those assumptions.

Sugihara used computer software to analyse seemingly impossible drawings and come up with solid shapes that might look like the drawing from one perspective, but not from others.

It's not the first time Sugihara has tricked New Scientist readers with his illusions. Earlier this year, the engineer won first prize in the 2010 Illusion of the Year contest in Naples, Florida.

And in June, New Scientistreported on a different approach to Escher-style illusions by Tai-Pang Wu at the Chinese University of Hong Kong.

That's why we're launching a brand new blog dedicated to bringing you the hottest science on screen. As well as bringing our breaking news stories to life, we'll be going behind the scenes to show you discoveries direct from the lab. From the latest advances in technology to the wonders of the natural world, you'll find it here on New Scientist TV.